1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same, and in particular, to a semiconductor device for controlling power used for a DC/DC converter, a digital audio amplifier, or the like, and to a method for manufacturing the same.
2. Related Background Art
A power MOSFET is used in applications in which it is necessary to reduce the switching loss in a high frequency band of a DC/DC converter, a digital audio amplifier, or the like as much as possible. If the switching loss is small, the amount of generated heat is small, and the electric power consumption is reduced. Therefore, for example, in portable electronics such as a notebook type personal computer and the like, the capacity of a built-in battery can be made small, and the entire apparatus can be made compact.
By the way, the shorter the switching time of the MOSFET is, i.e., the faster the switching speed is, the more the switching loss can be reduced. The switching speed depends on the gate charging amount at the time of switching, and the smaller the gate charging amount is, the faster the switching speed is. Accordingly, in order to make the switching of the MOSFET fast, it is necessary to reduce the gate capacity.
On the other hand, the channel resistance of the MOSFET is inversely proportional to the gate charging amount, and if the gate charging amount is small, ON-resistance arises. Further, if ON-resistance arises, the steady loss increases.
Further, in order to make the switching of the MOSFET fast, it is necessary to reduce the gate electrode width. If the gate electrode width is too large, because the withstand voltage of the MOSFET is reduced, from this stand point as well, it is necessary to reduce the gate electrode width.
On the other hand, from the standpoint of high integration, making the gate electrode interval, i.e., the interval between the gate electrodes, smaller has been required. However, from the standpoint of ensuring the withstand voltage of the MOSFET, an appropriate setting in the relationship with the gate electrode width is required.
As described above, conventionally, it has been difficult to attempt to make the switching speed fast, and to realize low electric power consumption while ensuring the withstand voltage of the MOSFET and suppressing the ON-resistance because of trading off various conditions.